Valves are widely used in fluid systems to provide controlled fluid flow behavior in the systems. Some valves utilized in high pressure drop applications or having large seat diameters may require pressure-balanced trim, typically including an actuator operatively connected to a valve stem assembly having a pilot head that extends into a small pilot area inside the valve plug between an open position and a closed position. The actuator urges the pilot head of the valve stem assembly away from the closed position, relieving the pressure in the cavity above the valve plug, and permitting the actuator to lift the entire valve plug using reduced force. When the pilot area is closed, the valve plug is sealed, preventing fluid flow therethrough.
With current valve stem assemblies, the pilot head is both threadedly engaged and welded to the valve stem, which welding may require subsequent heat treatment and re-coating, resulting in added fabrication and assembly time and cost. Additionally, the enlarged pilot head is acted on by fluid pressure that must be overcome by the actuator. Finally, the pilot head is prone to failure in field service.
What is needed is a valve stem assembly that does not suffer from these drawbacks.